You have to remember that, according to some genealogists and historians, many Irish are descended from Norwegians. I heard an historian at the Milwaukee Irish Fest some years back give a lecture where he basically said Brian Boru and his warriors were Norwegians who repelled other Norwegians at the Battle of Clontarf. He got a laugh from the people listening.
As I am well aware. Yet I was referring to the period of time in which clans took names, and towns were named for the clans living there. Coulter, the name, came from a Scottish clan/village. The Scots settlement of Ulster and the incursion of the Coulter clan into Ulster came many centuries after the Viking incursion into Ireland.