I've been looking for it for a couple of hours and I haven't found anything yet.
Can anybody tell me the keycode or the name of capacitive button with two squares in Android ICS?
It's the "Recent Apps" button, but to the best of my knowledge it's in the same category as the Home button in that it cannot and should not have its functionality overridden by a third-party application.
Even if it is possible to override, I would strongly advise against it.
See also: Handle Recent apps click, and KEYCODE_APP_SWITCH