You said — “I’ve never done this before, but the best way I can think of too scrub a hard drive forever is to expose it to a bearing heater for several minutes.”
If you’re serious about really destroying the data on a failed drive and are concerned about measures that a government can take to retrieve it — then I would break that platter up into pieces and obliterate it — and then get rid of the pieces in many different places, scattered around.
If you did that — it would end up just about 100% secure no matter what... LOL...
It really depends on how serious you are... :-)
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If it’s a working drive, you can use some effective scrubbers and ones that can really destroy the data and it can’t be retrieved (but it will take a while, a long while). Then you can use it again, without fear of the data being resurrected.