You could clear the browser history when the user logs out:
var url = window.location.href;
window.history.go(-window.history.length);
window.location.href = url;
However this would not be particularly robust - it relies on javascript, it would not work across multiple tabs and may only serve to annoy the user. IMO the best bet is to set appropriate caching headers such that the browser will not cache any of your 'logged in' pages via a NoCacheAttribute applied appropriately:
public class NoCacheAttribute : ActionFilterAttribute
{
public override void OnResultExecuting(ResultExecutingContext filterContext)
{
filterContext.HttpContext.Response.Cache.SetExpires(DateTime.UtcNow.AddDays(-1));
filterContext.HttpContext.Response.Cache.SetValidUntilExpires(false);
filterContext.HttpContext.Response.Cache.SetRevalidation(HttpCacheRevalidation.AllCaches);
filterContext.HttpContext.Response.Cache.SetCacheability(HttpCacheability.NoCache);
filterContext.HttpContext.Response.Cache.SetNoStore();
base.OnResultExecuting(filterContext);
}
}