Hey,
During my current game, some Settlers came sniffing around my territory. I clicked on an artillery unit, clicked the "boot", and then on the settlers. Volia - they were booted clean out of my territory. How nice.
Later, another race sent a settler in. I had three military units chase it about, trying to boot it. No luck. Boot boot boot
Finally, this settler moves into a place clearly in my boarders but NOT in my city radious and settles. Now I got a bunch of squatters.
So how does the boot function work?
BTW, I had good relationships (peace treaties and smiling faces) with BOTH nations.