It's CTRL+M, x,y,z , M will just open the layer-menue. CTRL+F is not necessary, in case there should be some normals pointing to wrong direction, try CTRL+N (recalculate outside) first. You can make normals visible in the Mesh Tools More panel in edit mode!!!

TheDaywalker :rock:
it's just M for me, and I find that CTRL+F works better as CTRL+N sometimes misses a few faces. I'm making the assumption that the mesh he's inverting already has normals all pointing in the right direction, so CTRL+F will be sure to hit them all.
EDIT: Okay, I checked, we're both right - it's CTRL+M when in Object Mode and M while in Edit Mode. I've been doing it in Edit Mode for the past many days (I've been making clothes), so I just quoted what I've been doing.