"If I move to WA, get new license, apartment etc in WA with no apartment/house/drivers license etc in CA wouldn't I be considered to be domiciled in WA?"
Tom is of course correct that a change of domicile would make you a nonresident of California. Note, however, that unless you move at midnight between December 31st and January 1st, you would need to file a part-year return for California for that part of the year in which you were living there.
Tom is also correct about this unique feature of California law that if you are a business (like a sole proprietorship, which a contractor is), then income generated from California clients is California source income and therefore taxable to California, even if you did the work elsewhere. This is different from most states who tax you where you work, not where your clients are.
So you will need to have a discussion with your employer about whether your relocation to Washington can be a permanent thing or not (or get a job in Washington).
