我是如下这样写的：

HttpCookie cookies = new HttpCookie("source");
        protected void Page_Load(object sender, EventArgs e)
        {
            if (cookies["source"] == null)
            {
                result = "Cookies 1";
                cookies["source"] = "pc";

                cookies.Domain = "www.testdomain.com";
                cookies.Expires = DateTime.Now.AddMinutes(30);
                
                HttpContext.Current.Response.Cookies.Add(cookies);
            }
            else
            {
                result = "Cookies 2";
                HttpContext.Current.Response.Write(cookies["source"].ToString());
            }
        }

现在我想知道应该如何让它持久化，因为当我关闭浏览器或者让这个页面默认跳转到另外一个网站（即另外一个域）后，我无法拿到Cookie