Emerging local synchrony / consensuses

Not in all systems global synchrony is needed or even desired. For example, in phone networks, we do not need to ensure that all participants of the network get the messages / packages ordered in the same way - we need only the ones which are involved in a conversation to comply to this constraint. All the others can by non-synchronous with respect to each other (until they need to synchronize). The system needs a mechanism for such local synchronise / consensuses to freely emerge when they are needed and dissolve when they are not needed.