Model driven engineering has become standard and important framework in software research field. Unified Modeling Language (UML) domain models are conceptual models which are used to design and develop software in software development life cycle. Models contain design level similarities, these are called model clones. Model clones are harmful for software maintenance as code clones and also lead to bad design. So number of clones need to be detected from UML domain models. Awareness of clones helps in reusable mechanism. Many techniques have been proposed for code clone detection but a few works has been done on model clone detection. In this paper, review has been provided related to various techniques for detection of clones in UML models.