The use of formal methods for verification and validation of critical and complex systems is important, but can be extremely tedious without modularisation mechanisms. SysML/KAOS is a requirements engineering method. It includes a goal modeling language to model requirements from stakeholder's needs. It also contains a domain modeling language for the representation of system application domain using ontologies. Translation rules have been defined to automatically map SysML/KAOS models into B System specifications. Moreover, since the systems we are interested in naturally break down into subsystems (enabling the distribution of work between several agents: hardware, software and human), SysML/KAOS goal models allow the capture of assignments of requirements to agents responsible of their achievement. Each agent is associated with a subsystem. The contribution of this paper is an approach to ensure that a requirement assigned to a subsystem is well achieved by the subsystem. A particular emphasis is placed on ensuring that system invariants persist in subsystems specifications