Commodity multicore systems are increasingly adopting hardware support that enables the system software to partition the last-level cache (LLC). This support makes it possible for the operating system (OS) to mitigate shared-resource contention effects on multicores by assigning different co-running applications to various cache partitions. Cache-clustering strategies have emerged as a way to improve throughput and fairness on platforms with cache-partitioning support. Unlike strict cache-partitioning, which allocates separate cache partitions to each application, cache-clustering allows partitions to be shared by several applications. In this article we propose LFOC+, a fair OS-level cache-clustering policy for commodity multicores. LFOC+ tries to mimic the behavior of the optimal cache-clustering solution for fairness, which we could obtain for different workloads by using a simulation tool. Our strategy continuously gathers data from performance counters to classify applications based on the degree of cache sensitivity and contentiouness, and separates cache-sensitive applications from aggressor programs to improve fairness, while providing acceptable throughput. We implemented LFOC+ in the Linux kernel and evaluated it on a system featuring an Intel Skylake processor, where we compare its effectiveness to that of four state-of-the-art policies. Our analysis reveals that LFOC+ brings a higher reduction in unfairness, and constitutes a lightweight cache-clustering policy.