Many network monitoring tasks identify subsets of traffic that stand out, e.g., top-k flows for a particular statistic. A Protocol Independent Switch Architecture (PISA) switch can identify these "heavy hitter" flows directly in the data plane, by aggregating traffic statistics across packets and comparing against a threshold. However, network operators often want to identify interesting traffic on a network-wide basis. To bridge the gap between line-rate monitoring and networkwide visibility, we present a distributed heavy-hitter detection scheme for networks modeled as one-big switch.We use adaptive thresholds to perform efficient threshold monitoring directly in the data plane. We implement our system using the P4 language, and evaluate it using real-world packet traces. We demonstrate that our solution can accurately detect network-wide heavy hitters with up to 70% savings in communication overhead compared to an existing approach with a provable upper bound.