Logout not working - Forms Authentication domain wide cookie

[Guest]

I'm using domain wide authentication cookie for single-signon solution.
Single signon is working fine but logout doesnt work. I tried using Signout()
method and also expiring cookie explicitely as follows but nothing works.
Please help.

System.Web.HttpCookie cookie;
string cookieName = System.Web.Security.FormsAuthentication.FormsCookieName;
cookie = Request.Cookies[cookieName];
cookie.Expires = DateTime.Now.AddDays(-1);
cookie.Domain = Citi.ASFP.Core.Utilities.WebUtility.GetDomain();
Request.Cookies.Set(cookie);
//Response.Cookies.Add(cookie);
Response.Redirect("login.aspx");

I used both Request.Cookies.Set(cookie) and Response.Cookies.Add(cookie)
with same results

Thanks in advance for your help !!!