It doesn't look like you can do it. If you deprovision, it will no longer be available through the enterprise management, so you wouldn't be able to push a powerwash. Likewise, if you powerwash first, it needs to be manually reconnected to wifi, which means you wouldn't be able to follow up with a deprovision.
This is where it talks about deprovisioning in the GAM wiki.
I hope this helps!