It's way better to include the cache-checking code in your application:
- Within your library, set a global variable (or a property of window object) to library's version number. The version number could be an increasing number, the date the change was made or (ideally) a version number from your source code control system (SCCS for Unix fans or Visual SourceSafe for Windows)
- In every web page that relies on particular functionality of that library, check the version number and force a reload if there's a mismatch.
window.version_MyLibrary = 20060810; // library last changed on August 10th, 2006
<script>if (window.version_MyLibrary < 20060810) location.reload(true);</script>