Circuitry comprises a set of data handling nodes comprising: two or more master nodes each having respective storage circuitry to hold copies of data items from a main memory, each copy of a data item being associated with indicator information to indicate a coherency state of the respective copy, the indicator information being configured to indicate at least whether that copy has been updated more recently than the data item held by the main memory; a home node to serialise data access operations and to control coherency amongst data items held by the set of data handling nodes so that data written to a memory address is consistent with data read from that memory address in response to a subsequent access request; and one or more slave nodes including the main memory; in which: a requesting node of the set of data handling nodes is configured to communicate a conditional request to a target node of the set of data handling nodes in respect of a copy of a given data item at a given memory address, the conditional request being associated with an execution condition and being a request that the copy of the given data item is written to a destination node of the data handling nodes; and the target node is configured, in response to the conditional request: (i) when the outcome of the execution condition is successful, to write the data item to the destination node and to communicate a completion-success indicator to the requesting node; and (ii) when the outcome of the execution condition is a failure, to communicate a completion-failure indicator to the requesting node.