public function touch($key, $expiration)
    {
        /**
         * touch <key> <exptime> [noreply]\r\n
         */

        // Build packet to send ...
        $data = self::COMMAND_TOUCH . self::COMMAND_SEPARATOR   .
            $key                    . self::COMMAND_SEPARATOR   .
            $expiration             . self::COMMAND_TERMINATOR;

        return $this->send(self::COMMAND_TOUCH, $data);
    }