You can empty a gemset, this will prompt you whether you are sure you wish to empty the gemset. This removes all gems installed to the gemset.

∴ rvm gemset use albinochipmunk
∴ rvm gemset empty albinochipmunk

If you wish to not be prompted, pass --force:

∴ rvm gemset use albinochipmunk
∴ rvm --force gemset empty albinochipmunk