Package-based Description Logics (P-DL) is a novel formalism for modular ontologies. In P-DL, an ontology is composed of a collection of modules called packages. A package can partially reuse knowledge in other packages by a selective importing mechanism. This paper investigates a sound and complete tableau-based reasoning algorithm for a P-DL language ALCPC, which extends ALC with acyclic concept importing between packages. The algorithm allows the reasoning process to be distributed based on local reasoning services offered by each module. The algorithm allows the reasoning process to be distributed based on local reasoning services offered by each module. Local tableaux associated with the ontology modules while physically separate, may conceptually overlap by communicating with each other via a set of messages. Our investigation shows the algorithm can avoid several semantic difficulties associated with existing approaches, such as transitive subsumption propagation and inter-module unsatisfiability detection.