I have factory reset my several times for different reasons. I always make sure when I go into "privacy" settings that I uncheck the restore options, bottom green check box then the top.
Go to the bottom and choose factory reset, you should not that one of the options in the factory reset has to do with the external SD card. I put one in so I check both and hit erase everything. That has been it for me. It should power off then reboot and format everything.