An interaction protocol specifies the constraints on communication between agents in a multiagent system. Ideally, we would like to be able to treat protocols as modules and compose them in a declarative manner to systematically build more complex protocols. Supporting composition correctly requires taking into account information-based causality relationships between protocols. One important problem that may arise from inadequate consideration of such relationships is that the enactment of a composite protocol may violate atomicity ; that is, some components may be initiated but prevented from completing. We use the well-known all or nothing principle as the basis for formalizing atomicity as a novel correctness property for protocols. Our contributions are the following. One, we motivate and formalize atomicity and highlight its distinctiveness from related correctness notions. Two, we give a decision procedure for verifying atomicity and report results from an implementation. For concreteness of exposition and technical development, we adopt BSPL as an exemplar of information causality approaches.