Source block
A conditional negative in a separate discovery lane after the harvested exact serves.
A source block can stop a proven query matching a separate discovery lane after its harvested exact starts serving. It requires later serving proof; if the exact never serves, the block expires.
Never put the negative in the destination ad group. It would suppress matching traffic for the exact you wanted to keep. If source and destination are the same ad group, withhold the source block. A duplicate alone does not prove higher auction prices or authorize blocking a different product's traffic.