If it fits, just run it through the pots and pans cycle of the dishwasher; nice and simple with great results. If not, soap and water will help, but if it's really gunked up you will get better results by using Simple Green. Finally, if it's really really really bad, get Muriatic acid from a masonry supply store and follow the directions on the bottle for cleaning bricks. Make sure to use gloves and goggles if using the acid. That is what many commercial gyms use and it removes chalk, oils, and shoe rubber (which you probably don't have on your fingerboard). Good luck.