public function flushExpired()
    {
        foreach ($this->_hashes as $name => $hashes) {
            foreach ($hashes as $key => $hash) {
                $cookie = $this->_data[$hash];
                if ($cookie->expired()) {
                    unset($this->_data[$hash]);
                    unset($this->_names[$hash]);
                    unset($this->_hashes[$name][$key]);
                    if (!$this->_hashes[$name]) {
                        unset($this->_hashes[$name]);
                    }
                }
            }
        }
        return $this;
    }