Purge chain if it shouldn't be there

agent/proxycfg/upstreams.go

@@ -47,8 +47,9 @@ func (s *handlerUpstreams) handleUpdateUpstreams(ctx context.Context, u cache.Up
 		switch snap.Kind {
 		case structs.ServiceKindIngressGateway:
 			if _, ok := snap.IngressGateway.UpstreamsSet[svc]; !ok {
-				// Discovery chain is not associated with a known explicit or implicit upstream so it is skipped.
+				// Discovery chain is not associated with a known explicit or implicit upstream so it is purged/skipped.
 				// The associated watch was likely cancelled.
+				delete(upstreamsSnapshot.DiscoveryChain, svc)
 				s.logger.Trace("discovery-chain watch fired for unknown upstream", "upstream", svc)
 				return nil
 			}
@@ -56,8 +57,9 @@ func (s *handlerUpstreams) handleUpdateUpstreams(ctx context.Context, u cache.Up
 		case structs.ServiceKindConnectProxy:
 			explicit := snap.ConnectProxy.UpstreamConfig[svc].HasLocalPortOrSocket()
 			if _, implicit := snap.ConnectProxy.IntentionUpstreams[svc]; !implicit && !explicit {
-				// Discovery chain is not associated with a known explicit or implicit upstream so it is skipped.
+				// Discovery chain is not associated with a known explicit or implicit upstream so it is purged/skipped.
 				// The associated watch was likely cancelled.
+				delete(upstreamsSnapshot.DiscoveryChain, svc)
 				s.logger.Trace("discovery-chain watch fired for unknown upstream", "upstream", svc)
 				return nil
 			}