Lately, my trusty Nexus 5 has been misbehaving-- lagging switching screens, etc. (gasp, behaving almost like my iPad 2!) so I uninstalled a few recent programs and decided to wipe the partition cache. But then I forgot how to this from Recovery mode and found this video to be the clearest explanation. When I tried to follow written instructions, I just couldn't get the phone to boot into the the appropriate screen. Keep in mind that the "-- Wiping cahce...Formatting /cache..." may actually take awhile-- the first tine I ever did this, it took about 20 minutes.