For dirty floor mats and many indoor/outdoor runner rugs and such, i have found a good scrubbing with simple green (using a bristle brush on a pole), letting it sit a while, and then using pressure washer with the “hover craft“ attachment (the spinning rotary cleaning device), works great. I do like the Atikovi idea of using the drill powered rotary brush to hit those concentrated stains.
I know that there will be those thinking “won‘t that damage the carpets?”. I’ve used the pressure washer method (set on the 2700-3000 psi setting) on the following with great results: lightweight foam-backed Honda floor mats, regular carpeted rubber-backed car mats, rubber backed runner carpets (such as those used in a mud-room or around the sink in the kitchen), outdoor carpets that are used on the deck and patio, and even our braided rugs that we have in the living room. You just have to be careful near the corners of lightweight mats/rugs as the rotary cleaner tends to “pop” the corner upwards where it can be impacted by the rotary head repeatedly. Other than that, have had great cleaning success on the stuff i have cleaned.
Very satisfying to see the muddy grime pushed up and out of the carpet fibers and floated away, particularly the first time you use this method or if it hasn’t been done in a few years.