I have some dupioni silk that I am going to be making a throw out of, with embroidered blocks. My mother has taken loads of classes from the Martha Pullen school, and does alot of the heirloom sewing (with silks and fine linens/cottons) She recommended the following for me:
1. If you want to wash the finished garment after it is complete, you must wash it prior to cutting. So if you want to dry clean, then dry clean the yardage. If you want to wash in washer, then wash the yardage prior. She recommended the "hand wash" option on your machine, with gentle soap. Probably baby soap would be good, they do sell fine heirloom quality soaps as well.
2. Dry till it is slightly damp, not fully dry but not dripping.
3. Iron gently, on back side with cool iron
4. Add a lightweight iron on woven interfacing to the back of the yardage BEFORE you cut. this will keep the fraying in check after cutting.
I helped wash/dry/press and cut some silk batiste that she used to make a dress for my niece. We followed the above recommendations *(except the interfacing, cause we lined with cotton batiste) and it worked out perfectly.