You cannot clear the cache, but you can ask that your pages will not be cached. This means that you must do so for every page in your session (else the back-button will keep working, and your logout page is the only page not cached).
See also: How to control cache in JSP page?:
httpResponse.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // HTTP 1.1. httpResponse.setHeader("Pragma", "no-cache"); // HTTP 1.0. httpResponse.setDateHeader("Expires", 0); // Proxies.
edit: Apparently it is possible to clear the cache programmatically using javascript and a refresh, but I doubt that this is what you are looking for: How to programmatically empty browser cache?