If the machine is company owned then the designation is usually whether the artifact or area of work is related to the main course of work. If you freelance in the same industry as your employer, you may have a tough time proving the distinction. Most of these agreements are only enforceable, though, when there's an overlap of work area regardless of who owns the machine. If the company is giving the employee the ability to use the hardware for personal use then the point of the hardware being company-owned is irrelevant to whether the work is being done on behalf of the company and, therefore, owned by the company.