Everyone remember when you could turn a core bright red by flipping its state?
Back in the old days, the memory bits were represented by single magnetic donuts - my recollection is about 3mm. These lil bits were weaved into a large plane with cross-wires. Apparently, flipping a single bit on and off fast enough (milliseconds?) would heat the poor thing up until it expired.
In the only slightly less old days, we were able to achieve the same thing (destruction of memory) by flipping a unit of memory (then called a "word") - probably using the wonderful XOR operation.
I guess there wasn't much use for something like Rowhammer back then.