I am sure there are places that clean down doonas properly but they are not cheap.
My Mum use to just throw ours in the machine with a mild detergent then hang them out on the line.

I have wanted to wash our goose down doonas because they have "that smell" about them but as I wash my linen weekly I just hang them on the line with the linen in full sun to air etc.

Nae x