Scrubbing hides is part of the process of tanning that turns hides into leather. A scrubber removes flesh, hair and such from the raw hides. It is a particular disgusting and hard labor. On Nilfeheim and until Eric and Elena change the process, tanning is done the old fashioned way without machines.
Nubhir Hide Scrubbers are among the lowest in the social hirachy of Nilfeheim. Nubhir Hide Scrubber is often used as an insult.