public static function expireCache( $contentClassAttributeID = false, $contentClassID = false)
    {
        unset( $GLOBALS['eZContentClassAttributeCacheListFull'] );
        if ( $contentClassID !== false )
        {
            if ( isset( $GLOBALS['eZContentClassAttributeCacheList'][$contentClassID] ) )
            {
                unset( $GLOBALS['eZContentClassAttributeCacheList'][$contentClassID] );
            }
        }
        else
        {
            unset( $GLOBALS['eZContentClassAttributeCacheList'] );
        }
        if ( $contentClassAttributeID !== false )
        {
            if ( isset( $GLOBALS['eZContentClassAttributeCache'][$contentClassAttributeID] ) )
            {
                unset( $GLOBALS['eZContentClassAttributeCache'][$contentClassAttributeID] );
            }
        }
        else
        {
            unset( $GLOBALS['eZContentClassAttributeCache'] );
        }

        // expire cache file by timestamp
        $handler = eZExpiryHandler::instance();
        $handler->setTimestamp( 'class-identifier-cache', time() + 1 );
        $handler->store();

        // expire local, in-memory cache
        self::$identifierHash = null;
    }