My Grandfather Lusk didn't have anyone "serve" him. He was the son of a farmer, who came to the U.S. in 1888 for a better life. He returned to Northern Ireland once, to settle his parents' estate and sell the farm, as he was an only son.
When I worked in a Boston bank, we had a summer intern from one of the Scandinavian countries, who said Lusk was a Scandinavian word meaning "bum"! However, in my trip to Lusk, Ireland, the brochure I was given there stated that it was derived from a Celtic word meaning "cave". Another derivation mentioned that it came from the name of the pagan god of light.