If you check the WSM, a 6.4 DPF is to be removed and cleaned at 200 000 km (ok 192 to be exact), and replaced at 400 000km. It also states the the DPF can only be cleaned once. This is to remove small amounts of soot/ash that are not removed by normal re-gen and can accumulate over time. I doubt any of these things ever lasts to 200k, but that's what the blue oval says. No as more wet contamination, I have no idea if that can be cleaned or not. I have removed DPFs for cleaning, but make sure you order the pressure sensor, the EGRT, the hardware kit, and the other nipple that will strip/break off. For those of you boys in the GTA, Peterbilt in Miss. on Eglinton will do this. Also A&A Exhaust in Hamilton offers the service, and will often pick up and delver.
Edit: Also I beleive they use a "Thermal" cleaning"