I've used one of those wet-type carpet cleaners before on previous trucks and it worked great. It's the type that shoots out the hot water/cleaner mixture and then sucks it up. We have one for our carpets that has the smaller attachment that's perfect for automotive use.
If you have nothing like that available, I'd hit it with a wet/dry vac and some automotive carpet stain remover.
Well no luck. I borrowed a buddies steam cleaner-no luck. I tried everything, nothing. 3 different carpet cleaners, baking soda, still there. The black Starbucks coffee must have some nasty stuff in it to dye the carpet.