Multicell joint decoding (MJD) has been widely studied during the last decades as a new communication paradigm which can overcome the interference-limited nature of cellular systems. From a practical point of view, a feasible solution is to exploit clusters of cooperating Base Stations (BSs) with intracluster MJD. However, the clusters would still be affected by intercluster cochannel interference. In this paper, the corresponding channel model is established incorporating four impairments, namely additive white Gaussian noise, flat fading, path loss and cochannel interference. The asymptotic capacity limit of this channel is calculated based on an asymptotic free probability approach which exploits the additive and multiplicative free convolution in the R- and Σ-transform domain respectively, as well as properties of the η and Stieltjes transform. Numerical results are utilized to verify the accuracy of the derived closed-form expressions and evaluate the effect of the cochannel interference.