I wouldnt cook all of the rock, but I would cook a little of it, *(if nothing else works) but do it slowly and a couple of pieces at a time. Cooking the rock will help break down the stored phosphates and it will also keep it detritrus free. Cyano loves dead spots where there is low flow. You might want to consider adding perhaps another powerhead with an indirect flow at the sand bed or wherever the cyano is growing. Do weekly water changes until the cyano is gone, and once it is gone do it for a couple of weeks more. Good luck with it and keep us posted.
Jerry
Jerry
Trying to get back in the hobby... Will be seting up my 75g rr soon