I don't know what this means Garfield Hts. PD Dispatch on TG 56557 and Law Talk TG 56558.
I'm new at this
It means that Garfield Hts. does not have a frequency. They are part of the Cleveland P25 Trunk System (GCRCN).
Each entity on a trunk system is assigned TG's (Talk Groups). They are virtual channels/frequencies. Each time a member of the Garfield Hts. PD key's their mike, the Trunk System Controller (computer) assigns the Talk Group to an available frequency. The Police radio's and our digital scanners receive the frequency information from the system controller.
W8RMH, posted a link to a Wiki that explains how trunk systems work.
I have a question for you. What kind/model of scanner do you have?