Nanoscale molecular clusters in cell membranes can serve as platforms to recruit membrane proteins for various biological functions. A central question is how these nanoclusters respond to physical contacts between cells. Using a statistical mechanics model and Monte Carlo simulations, we explore how the adhesion of cell membranes affects the stability and coalescence of clusters enriched in receptor proteins. Our results show that intercellular receptor ligand binding and membrane shape fluctuations can lead to receptor aggregation within the adhering membranes even if large-scale clusters are thermodynamically unstable in nonadhering membranes.