The Internet of Things (IoT) paradigm envisions a world of interconnected objects in which every object or thing can be univocally addressed and accessed, independently of its inherent technology and location. To the date, most of the state- of-the-art solutions proposed to realize the IoT vision employ a cloud-based approach. This means that, independently on where objects are physically located, their interconnection relies on a cloud-based solution. In a daily life situation it is like requesting a call-center operator to get us in contact to someone that is nearby us. Common sense tells us that it is not only simpler, but more efficient, to directly talk to him/her minimizing delays, failing points, and unnecessary intermediaries. This paper presents a protocol for IoT, named IDM (Inter-Domain Messaging), intended to overcome the limitations of cloud-based solutions for IoT. The IDM approach consists in offering an abstraction layer upon which different technologies can interact in a seamless and efficient manner. This paper also provides an experimental validation consisting in the implementation of a prototype inter- connecting five different domains, with technologies like ZigBee, Bluetooth, RS485 or WiFi.