public void completeIteration() {
        this.receiveMessages = this.sendMessages;
        this.sendMessages = new ConcurrentHashMap<>();
        this.previousMessageScopes = this.currentMessageScopes;
        this.currentMessageScopes = new HashSet<>();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/computer/TinkerMessageBoard.java