Hmmm... that must be different than the PS3 version because I remember trying that and there was still places in teh citities I couldn't go because of the dumb memory blocking thing
That's impossible, there are no more targets left. On Memory Block 6 you have everything unlocked, all three cities, Masyaf and the Kingdom to explore, best weapons and max throwing knives. Only once you attempt to kill the 'fake' Robert the map becomes limited to the road to Arsuf. To avoid it, just don't complete the mission and do whatever you want.