Nubuck is an extremely sensitive leather and we do not recommend that it is wet cleaned. You really need to use a napping brush and a Nubuck Cloth followed by a Nubuck Protector.
First do make sure it is Nubuck as there are so many fabric imitations on the market at present some of which are extremely deceptive.
It is always recommended that Nubuck is kept clean and protected from the start as it is very difficult to restore once it has got dirty. Any dark patches may well be grease which will not clean out and would have to be professionally restored.
Hope this helps
Judy