It depends on what your end goal is. For eg, you could have an indexer in your international site and have all your international forwarders send the data to that indexer. From there onwards the multisite clustering can take over and replicate the data to the US side.
The other way would be to have your international forwarders send the data to US indexers directly, eliminating the need to have an indexer in international site.
Irrespective of the options, the data needs to be transferred over the WAN. So it mainly depends on the amount of data and your network speed.