I add a teaspon of vinegar when I wash my cashmere. Also, I use one those high blast steam cleaners if I'm in a hurry. They barely get the cashmere wet, but it smells fresh as a daisy.
In between cleaning times I toss 2-3 pieces in the dryer with a fabric softener sheet and fluff dry for at least 5-10 minutes. Works great.
To infuse your own fragrance choice - use an unfragranced dryer sheet - lightly spray your favorite scent - and then toss in the dryer.
Cashmere can be hand-washed, dry-cleaned or washed on a wool setting in the washing machine. You can prolong the life of cashmere by wearing a vest/slip underneath, to reduce washing frequency. Use a mild detergent, always wash very gently in cool water and never wring the knit. Never use softener (this can "felt" the knit).Reshape the garment while it's damp,and dry flat on a plain towel.Store cashmere over the winter by wrapping in acid-free tissue and storing in boxes with cedar blocks/lavender to deter moths.
It wash my cashmere with Woolite or Ivory Snow (both made from sodium lauralte - the main ingredient in shampoo), a little white vinegar and a drop of my favorite scented body wash. It use cold water and I don't let them soak too long.
Always handwash cashmere in tepid water and mild detergent (I find Stanhome's Aquilaun is great, just a cap will do); soak no longer than 5 minutes; rinse thoroughly but gently; spin in the washing machine at high speed so as to get as much water away from the garment as soon as possible; you can then hang to dry (away from heat and sunshine if the color is light) as no extra weight will pull the garment out of shape. Steam iron. Store with lavender to deter moths.
I wash my cashmere jumpers in Belinda Robertson Cashmere Wash which is about 3 pound from Supermarkets in UK. Works really well, even better than dry cleaning and smells really nice.