An optimization based algorithm is proposed for solving elliptic problems with highly oscillatory coecients that do not exhibit scale separation in a subregion of the physical domain. The given method, written as a constrained minimization problem couples a numerical homogenization method in the subregion of the physical domain with scale separation with a ne scale solver in subregions without scale separation. The unknown boundary conditions of both problems in the overlap region are determined by minimizing the discrepancy of the corresponding solutions in this overlap.