How to erase stored data in MRAM memory devices
Writing is functionally equivalent to erasing.

Depending on the physical construction, writing may actually be a two step process, where the first step resets the memory to a "cleared" state, and the second step "sets" some of the bits.
Whether the state of a "cleared" bit is 0b11111111 or 0b00000000 is dependent on the specifics of the hardware.

Some memory, like flash, can only erase large sections of memory at once, so the process for "writing" to a byte may actually involve reading, and then storing a large section (It can be upwards of 512 bytes! This is called the "Page size"), and then updating the stored data (which is likely held in SRAM) with the new value, and then writing the updated data back to the page.

Anyways, from an IC-level perspective, this is largely irrelevant -
To "erase" something in the MRAM, you simply overwrite it with a new value.
If you want to make the erase option a separate step, simply write 0b00000000 or 0b11111111.