Single-Signin across servers in same domain

[Guest]

Hi,

I implemented Forms authentication for my apps (more than one). Since it'll
be hosted on a webfarm, I set cookie.domain = "nnn.nnn.com". This works fine.
I can signin and then go to other servers in same domain.

My problem is the Signout. I know FormsAuthentication.Signout() won't work
in this case. So I'm trying to explicitely expire authentication cookie. But
it won't signout and will come back every time. It's driving me crazy. Please
help. Code is given below:

code 1:
System.Web.HttpCookie cookie;
string cookieName =
System.Web.Security.FormsAuthentication.FormsCookieName;
cookie = Request.Cookies[cookieName];
cookie.Expires = DateTime.Now.AddDays(-1);
cookie.Domain = "xxx.xxx.com";
cookie.Path = FormsAuthentication.FormsCookiePath;
Response.Cookies.Add(cookie);
Response.Redirect(Request.UrlReferrer.ToString());

I tried this also but no use:
System.Web.HttpCookie cookie;
string cookieName =
System.Web.Security.FormsAuthentication.FormsCookieName;
int count = Request.Cookies.Count;
for(int i=0; i < count; i++)
{
cookie = Request.Cookies;
if(cookie.Name.Equals(cookieName))
{
cookie.Expires = DateTime.Now.AddDays(-1);
cookie.Domain = "xx.xxx.com";
cookie.Path = FormsAuthentication.FormsCookiePath;
Response.Cookies.Add(cookie);

}
}

Response.Redirect("/app/main.aspx");