How to get rid of washing powder stains on dark cashemere clothes?

[ValeriaS]

I hand washed 2 dark items - one 100% cashemere, the other half silk, half cashmere. It was dry clean only but I decided to risk it, really shouldn't have. They both have soap residue which I just cannot wash out. Any tips? TIA!

Thanks, TirednessKills! Already tried that - both by hand and in the machine. I should have used Woolite but used normal powder. :-( I just thought that someone might know a trick - like 'rinse it with vinegar' type of thing :-)

I use shampoo for wool and silk.
I would leave in cold water for a bit and rinse out again.