The problem is that the sharp knives have caused many cuts all over on my plastic chopping board. Now, I can see the minute vegetable remains in the cuts on board.  What's the way to "easily" get the dirt out of those cuts? 
If the dishwasher and hand-scrubbing cannot remove stains, professionals sometimes use a simple solution:  we apply pure bleach directly to the board and scrub it in with a stiff-bristled plastic brush.  Then we allow the bleach to sit for 5-10 minutes.  At this time, most stains are gone or almost gone. Then we clean the board THOROUGHLY until no bleach smell remains.  Usually it takes 2 cycles in a dishwasher or hand scrubbing and rinsing several times.  This method is extremely fast and effective, particularly for troublesome vegetable stains (beets, carrots, chopped herbs). 