Completely aware of their existence, in both directions. This comment I wrote a while ago discusses the extent to which Jews were in touch with each other throughout the world as far back as the 1200s (as I recall the other answer to the question I answered there was also very good), and there had been communication far further back than that, as the Babylonian Jewish community and the Talmudical academies there were seen as the linchpin holding world Jewry together. The communities never really lost touch with each other or awareness of each other after that.

What KIND of relationships these communities had is a different question, and one that I would love to return to but just don't have time to right now. I'll do my best to, though, at a later point.