How to thoroughly clean this?

This bread board has been in the family for longer than I have been (18 years atleast). Its always been there. If it get bad we rinse it under running water. The black thing is from a toast I might rightnow that was slightly (very) charred because I forgot it.

Now with all the chipping and what not, how can I thoroughly clean the board. I'd imagine there to be a lot of not immediately observable gunk.