L1 entries should be invalidated when the key ownership changes

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[...] we have thought about actually transferring the requestor information with the transaction data, but that gets complicated really quickly. (It would most likely require forwarding get commands, which would negate the benefit of having an L1 in the first place.) Instead we are going to remove L1 entries that have lost owners on each topology update (which should be a small fraction of the total L1 entries).