In fog computing customers' microservices may demand access to connected objects, data sources and computing resources outside the domain of their fog provider In practice, the locality of connected objects renders mandatory a multi-domain approach in order to broaden the scope of resources available to a single-domain fog provider. We consider a scenario where assets from other domains can be leased across a federation of cloud-fog infrastructures. In this context, a fog provider aims to minimize the quantity of external resources to be rented to satisfy the applications' demands while meeting their requirements. We first introduce a general framework for the deployment of applications across multiple domains owned by multiple cloud-fog providers. Hence, the resource allocation problem is formulated in the form of an integer linear program. We provide a novel heuristic method that explores the resource assignment space in a breadth-first fashion to ensure that locality constraints are met. Extensive numerical results evaluate deployment costs and feasibility of the proposed solution demonstrating that it outperforms the standard approaches adopted in the literature.