Connecting two iMacs over thunderbolt: is there a shortcut key to disconnect them?

I decided rather than buy a thunderbolt display I'd just grab another iMac, since I was able to find one in mint condition for close to the cost of an Apple display. Kind of a no brainer. Anyhow, so far so good. When I hit cmd + f2 it makes the current machine the external of the other, and cmd + f1 switches between mirroring and extended. Anyhow, is there a way to switch back to separate machines? cmd + f2 doesn't toggle, or is the only way to do this to reach around behind and yank the plug?

Ok, I solved my problem. Basically the issue is called exiting target display mode. What happens is iMacA is given the cmd +f2 which makes it a target display for iMacB. If iMacA is set to require a password to wake from sleep this will interfere with exiting target disk mode. You can do it by typing your password on the keyboard of iMacA and then hitting cmd + f2. The best solution is to shut off the password requirement for waking from sleep and then you can switch between target display mode and having both machines as separate. Very cool.