A few years ago we had the job of cleaning just that from the walls of a chain smoking elderly Aunts house.
We used a detergent called Vee Vic, that was sold as a decorators cleaner like a heavy duty version of sugar soap. It worked, but i havent seen this product around recently. You could ask in a good painters suppliers, I dont mean a DIY shop!
Or you could try Vulpex, which the museums seem to use for everything. You get this from conservators suppliers. Do a Google for it.
John