'what is clean?' I think of the word clean as I do the word pain :
If I have a pain in my tooth I can take aspirin and the pain will still be there but because of the aspirin I won't feel it, BUT THE PAIN IS STILL THERE.
The same goes for 'clean' I can use chemicals to make the dirt appear to go away, but it is still there.
CLEAN Free from dirt or contaminating matter ( The Oxford compact English Dictionary)
When I clean a carpet I use a softened freshwater rinse So I believe I leave the carpet in the most clean, free from foreign matter state possible.
I think a lot of carpet cleaners actully just swop the contaminants or cleverly hide them
Mike