It seems there are already some bugs logged (and closed) regarding this issue. See https://bugzilla.redhat.com/show_bug.cgi?id=632391 and https://bugzilla.redhat.com/show_bug.cgi?id=628963
In the meantime however, if you want to safely clear up the useless data in /var/cache/yum, you can just run the following command:
yum clean all |
For me it went from 8Gb of useless sqlite files to none in 2 seconds.