Another possibility is soaking the board in a bleach-and-water solution overnight. Put the board in a container in which it can be covered with the liquid, and let it sit. The grime may or may not be loosened, but it will certainly be neutralized.
I would go into the kitchen at the country club several mornings a year and find all the cutting boards soaking in the sink in water and bleach, but still, the gm would have them all thrown out at the beginning of the next season and buy new ones. I use wood, keeping a piece of corian that fits in the sink for poultry and a small wooden board for garlic and ginger and onions.
Well from all the great suggestions I suppose that I should first, soak the boards in bleach & water, second, use a scrub brush with soda, then if that doesn't work, either toss them out or have them re-planed!
I really appreciate all of the help, if I have any luck at this I'll post it!
Some academics at the Univ. Of Wisconsin Department of Food Sciences did a study of cutting boards and concluded that wood boards were much more sanitary than plastic ones.
The bacteria stayed on the surface of the plastic boards - and in the knife grooves - and survived pretty well. They soaked into the wood boards... and died.
Cabinet scrapers are a whole 'nother set of techniques. You have to buy one (it's cheap, just two or three dollars from a place like www.LeeValley.com) but then you need a carbide burnisher (not quite so cheap) to put an edge on the scraper, and a vice to hold it while you square the edge of the scraper with a file and re-form the edge with the burnisher and...
hey... just use a good end-grain cutting board. Your knives will thank you for it.
We have the Health Board all over us for this, I bleach the boards every night and they still complain. I am now looking into a new material that apparently does not scuff or mark, going to get the line all replaced and the back prep counter. I will fill you in when I get it in.