The funny thing is that when Islamic Spain was at its height culturally (not territorially), there was no overall caliphate. The Muslims world was split up into maybe three differnt parts even them. I know you had the Fatimids in Egypt, who was ruling Iraq? (see, I thought the caliphate was originally based somewhere in Iraq), and a couple of dynasties ruled N. Africa and Spain. One caliph running the whole of the Islamic world probably ceased in the 900s or so.
Damascus?