You can safely wash cashmere.  I have washed my cashmere sweaters by hand many times with woolite detergent and the results are fine.  There is information on how to hand wash cashmere and other sweaters online if you are not sure,  just do a search on how to safely wash cashmere. 

I am an avid hand knitter. When I was taking my beginning knitting class, they told us that the preferred method for cleaning cashmere or wool is hand washing with an appropriate shampoo with cool water and then lie flat and let air dry. A company called Laundress makes a good shampoo for sweaters. It’s gentler than dry cleaning.

But machine washing is a don’t. So is washing with hot water at it will call the sweater to felt.