Shame on me. I've stopped using toe in as a way of stopping brake shriek. I spray a little teflon on a cloth, wipe both sides of rim et volia. Problem solved and in 99% of cases doesn't return. I use it on customers bikes (although mainly V-brake equipped)

Slightly diminished braking power the first couple of times, but I take care of that by doing that for the customer on the test ride.

It is my experience that cleaning the rim sidewall to within an inch of its life is often the cause of the problem, not the solution.