A network of switches that forwards network packets between end hosts may be controlled by a controller. The controller may maintain information that identifies subsets of the end hosts that are associated with respective broadcast domains. The controller may use network topology information to determine which of the switches are coupled in a forwarding tree formed from network paths between the end hosts of a broadcast domain. The controller may be used to configure the switches with an identifier that identifies which broadcast domain is associated with each subset of end hosts. The controller may configure switches of a given forwarding tree that are coupled to end hosts of an associated broadcast domain to modify broadcast network packets received from the end hosts with the identifier and to forward the modified broadcast network packets along the forwarding tree exclusively to end hosts of the associated broadcast domain.