There is some info on this, I asked it a while ago, check this thread: http://forum.beoworld.org/forums/t/35662.aspx
There's a lot more, check the search function for rosewood.
First remove fat with white spirit or something like that, then sanding with 1000 grit paper, then apply rustins Danish oil, it works wonders. If you have to sand deep to get scratches out you might get to a layer of wood with less color, you could try rustin's wood dye for that, the red mahogany version, but I have no experience with that!
Good luck!