How do you know what is driving the bus, MMU ? CPU ? Buffers ? DRAM ? Even a cut track will still be driven by something. Even a floating signal can still give a voltage. So the tests are just not valid. Even with a scope its very hard to debug.
If the MMU can't get correct data back from the DRAM, it marks the bank as bad. Regardless of what you measure, how do you know what bits are faulty internally on the DRAM chips ?
Adding more potential issues onto a board which is already malfunctioning isn't a good idea.