LazySweeper
This is certainly one of the easiest solutions for the second hardest thing in computer science. It is based on a post by Thijs at Fingertips.
Have fun sweeping your entire page cache.
Add models by calling LazySweeper.observe in an initializer. You can also call LazySweeper.run manually if needed.
For more information, you can check the Rails Envy article on page caching that also ripped the original code.