This paper introduces Nemo, a novel peer-to-peer multi-cast protocol that aims at achieving this elusive goal. Based on two techniques: (1) co-leaders and, (2) triggered negative acknowledgments (NACKs), Nemo's design emphasizes conceptual simplicity and minimum dependencies, thus achieving, in a cost-effective manner, performance characteristics resilient to the natural instability of its target environment. Simulation-based and wide-area experimentations show that Nemo can achieve high delivery ratios (up to 99.98%) and low end-to-end latency similar to those of comparable protocols, while significantly reducing the cost in terms of duplicate packets (reductions > 85%) and control related traffic, making the proposed algorithm a more scalable solution to the problem.