Jesper Fabricus has provided a good answer. Worded slightly differently, one of the DVs could become a mediator variable, a variable through which the IVs act upon the 2nd DV; e.g., IVs--> DV1 --> DV2 such that the IVs have no little or no direct influence on DV2. The classic article on the logic of mediation versus moderation, including how to test for mediation in a variety of designs, is Baron, R. M., & Kenny, D. A. (1986). The moderator-mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. Journal of Personality and Social Psychology, 51(6), 1173-1182.