Many manufacturers recommend that you dry clean your cashmere jumper because very few people know how to wash them and they get sick of customers complaining that their lovely expensive jumpers have shrunk or been ruined.
Cashmere HATES hot water and too many soap suds.
You can clean your cashmere knitwear in COLD water (not warm) COLD. You can add a LITTLE detergent. If you have a grubby spot on the item, just rub that with soap and rinse out and then wash the whole item.
Rinse thoroughly - with COLD water - and I mean COLD. When rinsed - lie it flat on top of a towel in a well aired room. Once dry you can iron.
It's so easy, this is how you should wash all natural fibres. Natural fibres like cashmere, lambswool, merino etc are pretty easy to take care of, its often the fibre of the stitching that will shrink or change the shape of lets say a wool suit, so don't try washing that in cold water. IF IN ANY DOUBT - DRY CLEAN !