A simple solution could be a very short JavaScript blanking fields and, optionally, setting a new URL.
The essential code can be found at
http://community.marketo.com/MarketoArticle?id=kA050000000KysDCASThe URL cab be set using, among other options,
1. self.location=”login.html”;
2. // similar behavior as an HTTP redirect
window.location.replace("http://company.com/login.html");
3. // similar behavior as clicking on a link
window.location.href = "http://company.com/login.html";