diff --git a/cache/classes/config.php b/cache/classes/config.php
index 682ef181491..da3b9665915 100644
--- a/cache/classes/config.php
+++ b/cache/classes/config.php
@@ -344,6 +344,61 @@ class cache_config {
         return $this->configdefinitions;
     }
 
+    /**
+     * Returns the definitions mapped into the given store name.
+     *
+     * @param string $storename
+     * @return array Associative array of definitions, id=>definition
+     */
+    public static function get_definitions_by_store($storename) {
+        $definitions = array();
+
+        $config = cache_config::instance();
+        $stores = $config->get_all_stores();
+        if (!array_key_exists($storename, $stores)) {
+            // The store does not exist.
+            return false;
+        }
+
+        $defmappings = $config->get_definition_mappings();
+        // Create an associative array for the definition mappings.
+        $thedefmappings = array();
+        foreach ($defmappings as $defmapping) {
+            $thedefmappings[$defmapping['definition']] = $defmapping;
+        }
+
+        // Search for matches in default mappings.
+        $defs = $config->get_definitions();
+        foreach($config->get_mode_mappings() as $modemapping) {
+            if ($modemapping['store'] !== $storename) {
+                continue;
+            }
+            foreach($defs as $id => $definition) {
+                if ($definition['mode'] !== $modemapping['mode']) {
+                    continue;
+                }
+                // Exclude custom definitions mapping: they will be managed few lines below.
+                if (array_key_exists($id, $thedefmappings)) {
+                    continue;
+                }
+                $definitions[$id] = $definition;
+            }
+        }
+
+        // Search for matches in the custom definitions mapping
+        foreach ($defmappings as $defmapping) {
+            if ($defmapping['store'] !== $storename) {
+                continue;
+            }
+            $definition = $config->get_definition_by_id($defmapping['definition']);
+            if ($definition) {
+                $definitions[$defmapping['definition']] = $definition;
+            }
+        }
+
+        return $definitions;
+    }
+
     /**
      * Returns all of the stores that are suitable for the given mode and requirements.
      *
diff --git a/cache/classes/helper.php b/cache/classes/helper.php
index 154d9d86472..d6723901b08 100644
--- a/cache/classes/helper.php
+++ b/cache/classes/helper.php
@@ -389,16 +389,9 @@ class cache_helper {
      */
     public static function purge_all() {
         $config = cache_config::instance();
-        $stores = $config->get_all_stores();
-        $definition = cache_definition::load_adhoc(cache_store::MODE_REQUEST, 'core', 'cache_purge');
-        foreach ($stores as $store) {
-            $class = $store['class'];
-            $instance = new $class($store['name'], $store['configuration']);
-            if (!$instance->is_ready()) {
-                continue;
-            }
-            $instance->initialise($definition);
-            $instance->purge();
+
+        foreach ($config->get_all_stores() as $store) {
+            self::purge_store($store['name']);
         }
     }
 
@@ -410,21 +403,32 @@ class cache_helper {
      */
     public static function purge_store($storename) {
         $config = cache_config::instance();
-        foreach ($config->get_all_stores() as $store) {
-            if ($store['name'] !== $storename) {
-                continue;
-            }
-            $class = $store['class'];
+
+        $stores = $config->get_all_stores();
+        if (!array_key_exists($storename, $stores)) {
+            // The store does not exist.
+            return false;
+        }
+
+        $store = $stores[$storename];
+        $class = $store['class'];
+
+        // Found the store: is it ready?
+        $instance = new $class($store['name'], $store['configuration']);
+        if (!$instance->is_ready()) {
+            unset($instance);
+            return false;
+        }
+
+        foreach ($config->get_definitions_by_store($storename) as $id => $definition) {
+            $definition = cache_definition::load($id, $definition);
             $instance = new $class($store['name'], $store['configuration']);
-            if (!$instance->is_ready()) {
-                continue;
-            }
-            $definition = cache_definition::load_adhoc(cache_store::MODE_REQUEST, 'core', 'cache_purge');
             $instance->initialise($definition);
             $instance->purge();
-            return true;
+            unset($instance);
         }
-        return false;
+
+        return true;
     }
 
     /**