When cleaning the oven because it is round, you want to use a curved amber rake. Really gets in the corner and also helps moving around the embers / wood.http://www.breadstoneovens.com/collections/cooking-tools/products/embers-rake
Yes, I am a vendor not pushing my product, it just works better, buy it from whom ever you want. I just want to make sure you get the right tool. The "T" shaped ember rakes I have found to not work as well.
Then a bristle wire brush like the one Craig suggested is good. Just make sure the head can be easily replaced.
You can rake the ember and ashed out of your oven or use a shovel.