private function _delete($filename, $directory = null)
    {
        $cache_path = $this->config->get('cache_path');

        if (is_null($directory)) {
            $path = $cache_path.$this->config->get('object_dir').$filename.'.cache';
        } else {
            $path = $cache_path.$directory.$filename.'.cache';
        }

        // nope. not here.
        if ( ! file_exists($path)) return true;
        return (bool) unlink($path);
    }