Symbolics (and other systems like it) had typed memory with hw type checking (so you had safe memory by default), and had one important bit for efficient GC (one that is also utilized by Azul and Shenandoah) - forwarding pointers, in their case implemented "transparently" to actual code.

With forwarding pointer, you can copy data and update a reference in a way that is transparent to concurrently running code, as when it access the data again the CPU (or software implementation) will notice the data had been moved and follow the forwarding pointer to new location.

The rest of the support for GC was centered around structure of virtual memory, without anything very specific to GC in hw - we're talking about things like "memory is divided into X areas, inside each area the lower side is ephemeral... " etc. There was also some register use to keep track of GC status. I think some versions had MMU or page fault handler update the GC register data.