Synchronization Scope Activity
The Synchronization Scope Activity can hold a sequence of activities in the same way as a Sequence Activity, but also guarantees uninterrupted execution. When used within activities that have parallel execution paths; such as the Parallel, Replicator, and Conditional Activity Group activities; the Synchronization Scope Activity provides an explicit way of modeling synchronized access of shared resources. The SynchronizationHandles property provide a way to do this by means of a comma separated list of identifiers.
For more information and an example see Workflow Basics – Synchronization Blocks.