"Chemically cleaned" might mean one of the chains (such as Chem-Dry) who don't use steam/hot water but rather use a cleaning chemical that dries on the carpet. THIS IS A TERRIBLE PROCESS! The carpets are left with a soapy/sticky residue that feels awful and attracts and collects dirt much faster than a conventionally cleaned carpet. We purchased a house about seven years ago that had been done by Chem-Dry... it took a Stanley Steemer supervisor three passes to get all the cr@p out of the carpets. We now own our own deep cleaner that does a very good job. It uses small amounts of hot water with a minute amount of carpet cleaning solution. After the initial cleaning, a plain water rinse is used to make sure any residual cleaner is removed from the fibers. It has a hose with attachments (separate from the upright head for the large areas) for doing hard-to-reach places, upholstery, etc.
Again - avoid so-called chemical cleaning outfits like the plague.
Rob