What is the safest way to logout of a forms authenticated web app?

To Logout of my web app, I use:
Session.abandon()
FormsAuthentication.SignOut()
Response.Redirect("url")
 
"url "just redirects back to my login page.   The problem is that I periodically get "too many redirects" from the browzer and found that if I ever try to login in from a different browser tab while the "url" is still open,  then I will get this error.  I close the tab, and the problem usually goes away.  So even though I am abandoning the sesion, and clearing out the authentication, something is still sticking around.
Any ideas?
Thanks!
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