public void purgeBlocksOlderThan(final long blockNumber) {
    pendingBlocks.values().stream()
        .filter(b -> b.block().getHeader().getNumber() < blockNumber)
        .map(ImmutablePendingBlock::block)
        .forEach(this::deregisterPendingBlock);
  }
Stop tracking the given block.

@param block the block that is no longer pending
@return true if this block was removed
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/state/PendingBlocksManager.java