The Cloud-based infrastructure-as-a-service (IaaS) paradigm (e.g., Amazon EC2) enables a client who lacks computational resources to outsource her dataset and data mining tasks to the Cloud. However, as the Cloud may not be fully trusted, it raises serious concerns about the integrity of the mining results returned by the Cloud. To this end, in this paper, we provide a focused study about how to perform integrity verification of the κ-means clustering task outsourced to an IaaS provider. We consider the untrusted sloppy IaaS service provider that intends to return wrong clustering results by terminating the iterations early to save computational cost. We develop both probabilistic and deterministic verification methods to catch the incorrect clustering result by the service provider. The deterministic method returns 100% integrity guarantee with cost that is much cheaper than executing κ-means clustering locally, while the probabilistic method returns a probabilistic integrity guarantee with computational cost even cheaper than the deterministic approach. Our experimental results show that our verification methods can effectively and efficiently capture the sloppy service provider.