Удаляем куку

/**
    * удаляем куку с именем $cookieName
    * @example 
    *   $this->clearCookie("DISCOUNT_NO");
    *         
    */
    protected function clearCookie($cookieName)
    {
        $negativeTime = 3600*24*10;
        setcookie($cookieName, '', time() - $negativeTime,"/");
    }