Clearing the gem source_cache in Ruby

I was trying to install a Ruby Gem when I got the following error message:

ERROR:  While executing gem ... (Gem::GemNotFoundException)
    Could not find xhtmldiff (> 0) in the repository

Googling around, I found out that this error may mean that the source cache is corrupt. Sure enough, that was the problem.

To fix it, under Locomotive, I deleted the following file:


And that fixed it! :)