MD soft-raid to replace fake raid: How to get rid of old metadata?

I had a system running with fake RAID (Intel controller, imsm), which had some problems. Now I'm switching to the regular MD soft-RAID - I created a RAID 1 on /dev/sda1 and /dev/sdb1. Seems to work fine. Unfortunately a run of mdadm --examine /dev/sd[ab] shows that I still have the Intel metadata sitting on top at /dev/sda and /dev/sdb. The metadata of the soft-RAID is only stored within sda1 / sdb1. How can I get rid of the Intel data, without breaking anything?