Just ran accross a good blog post on how to clear IE's SSL Session Cache, this is useful if you want to have a "logoff" button on a website that uses mutually authenticated SSL.
Specifically a new execCommand was added in to enable this:
// Clear current credentials
// Requires IE6 SP1 or later
document.execCommand("ClearAuthenticationCache", false)
Check it out: http://www.adopenstatic.com/cs/blogs/ken/archive/2005/04/12/14.aspx