Is log flush for a cr block transfer required ?

In a 2-node RAC environment we know that the gc current block service time is composed of "pin time + flush time + send time". Flush time means that redo of the current block modified on the remote instance must be written to redolog before LMS can transfer it to the requesting instance. That's easy to understand.

But As concerns gc cr block service time, it is also composed of "pin time + flush time + send time".

Since the requested block is a CR block which have not produced any redo and it's even not necessary to flush any redo to disk. But why "flush time" would still count for "gc cr block service time" ?