You have several options (many more than for the static building block view..). The following list is ordered by increasing documentation and maintenance effort. Options further down that list are more fine-grained and usually contain more details.
- Document scenarios in plain text by enumerations or numbered lists. Include precise hints which building block executes which step(s) of use cases, processes or functions.
- Use activity diagrams or flowcharts with swim-lanes.
- Use UML sequence diagrams. They can be time-consuming to create and maintain with most interactive tools, but are an excellent means to show the mapping between building blocks and their actions. See question F-10 (tools for sequence diagrams) for some tips on tools.
UML has some additional options (e.g. state transition or object diagrams) to describe behavioral aspects of systems or building blocks. Those can be sometimes be useful, but are less often used that activity- or sequence diagrams.