You can create a dependency between a cached page and a file (or set of files) on your hard drive.
When the file is modified, the cached page is automatically dropped and regenerated with the next page request.
<%@ Page Language="C#" %>
<%@ OutputCache Duration="9999" VaryByParam="none" %>
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Output Cache File Dependency