A method of operating a content delivery system comprising content delivery nodes configured to cache content for delivery to end user devices, the method comprising: responsive to requests to purge the content cached by the content delivery system, transferring purge messages for delivery to each of the content delivery nodes; the method characterized by: in the content delivery nodes, if the purge messages are received, purging content associated with the purge messages and compiling purge summaries which indicate the purge messages that are received; in the content delivery nodes, transferring the purge summaries for delivery to one or more other content delivery nodes, of the content delivery nodes; in a first of the content delivery nodes, receiving a first purge summary transferred by a second of the content delivery nodes, and comparing the first purge summary to a second purge summary maintained by the first content delivery node to identify one or more missing purge messages that have not been implemented by the first content delivery node; and in the first content delivery node, responsive to identifying the one or more missing purge messages, requesting purge details associated with the one or more missing purge messages from the second content delivery node and implementing the one or more missing purge messages once the purge details have been received by purging content associated with the one or more missing purge messages, wherein the purge details include information to implement the purge specified by the one or more missing purge messages. responsive to requests to purge the content cached by the content delivery system, transferring purge messages for delivery to each of the content delivery nodes; the method characterized by: in the content delivery nodes, if the purge messages are received, purging content associated with the purge messages and compiling purge summaries which indicate the purge messages that are received; in the content delivery nodes, transferring the purge summaries for delivery to one or more other content delivery nodes, of the content delivery nodes; in a first of the content delivery nodes, receiving a first purge summary transferred by a second of the content delivery nodes, and comparing the first purge summary to a second purge summary maintained by the first content delivery node to identify one or more missing purge messages that have not been implemented by the first content delivery node; and in the first content delivery node, responsive to identifying the one or more missing purge messages, requesting purge details associated with the one or more missing purge messages from the second content delivery node and implementing the one or more missing purge messages once the purge details have been received by purging content associated with the one or more missing purge messages, wherein the purge details include information to implement the purge specified by the one or more missing purge messages. in the content delivery nodes, if the purge messages are received, purging content associated with the purge messages and compiling purge summaries which indicate the purge messages that are received; in the content delivery nodes, transferring the purge summaries for delivery to one or more other content delivery nodes, of the content delivery nodes; in a first of the content delivery nodes, receiving a first purge summary transferred by a second of the content delivery nodes, and comparing the first purge summary to a second purge summary maintained by the first content delivery node to identify one or more missing purge messages that have not been implemented by the first content delivery node; and in the first content delivery node, responsive to identifying the one or more missing purge messages, requesting purge details associated with the one or more missing purge messages from the second content delivery node and implementing the one or more missing purge messages once the purge details have been received by purging content associated with the one or more missing purge messages, wherein the purge details include information to implement the purge specified by the one or more missing purge messages.