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Synchronous domains need to be balanced during CTS. If one frequency is a multiple of another, then the design must ensure the faster domain does not sent data faster than the slower domain can handle.
If it's synchronous and the same frequency, then you don't need to do anything. If it's synchronous but the frequencies are multiple of each other, then you need to stretch the fast clock's signals to match the slow clock's frequency or else you might not be able to latch it correctly.
Some of the responses are for data transfer across an ASYNCHRONOUS clock domains, so you can ignore them.
It's important to ensure that data is not sampled on or near clock edges where it might change. If two domains have clocks that are "almost" perfectly in sync, you should have data leaving each domain change on the opposite clock edge from where it will be sampled in the other. To minimize "round trip" lag, it may be helpful to, if you can, have the two domains operate on opposite clock edges from each other. That way, the delay when passing between domains would be a half clock rather than a full clock.